Validity of esophageal pressure measurements with positive end-expiratory pressure in preterm infants.

Previous research suggested that esophageal pressure changes (DeltaP(es)) may not reflect pleural pressure changes (DeltaP(pl)) in the presence of positive end-expiratory pressure (PEEP), making assessments of dynamic lung mechanics invalid in these circumstances. To test this hypothesis, we measured DeltaP(es) using a water-filled catheter in 18 preterm infants with lung disease (9 intubated), and adjusted the catheter position to achieve a valid occlusion test. End-expiratory occlusions were then carried out at PEEP (cm H(2)O) of 0, 4, and 8, and plots of DeltaP(es) against DeltaP(ao) during airway occlusion were examined to derive the ratio DeltaP(es)/DeltaP(ao) and the r value (as a measure of linearity). There was no significant change in DeltaP(es)/DeltaP(ao), which remained close to 1.0 as PEEP was increased from 0 to 8 cm H(2)O, and r also remained close to unity, indicating no appreciable hysteresis or alinearity of the plots. Our results show that DeltaP(es), when measured with an appropriately placed water-filled catheter, continues to reflect DeltaP(pl) accurately when lung volume is raised by applying PEEP up to 8 cm H(2)O.